Add autocompletion for imported functions

[yaksher]

Would it be possible to have code completion for functions from imported modules (at least local ones) like you get for builtin commands and those defined inside the current file?

This might be a bug report rather than a feature request, but I figured I'd err on the side of saying it's a feature request.

[nvarner]

This will be added via Typst v0.9.0 support, which should appear in a release soon.